How Planets Get Moons

Drilling into Earth’s Mantle

Turns out it was much easier to go to outer space than to inner Earth. In the 1950s, the U.S. and Russia began competitive spaceflight programs. Twenty-five years later, the U.S. Voyager spacecraft had gone 10 billion miles into space. Around the same time, both countries also began drilling programs trying to pierce through Earth’s crust to reach the mantle below. The U.S. project began drilling off the coast of Mexico, because scientists had recognized that oceanic crust is thin, averaging only 4 miles thick, whereas continental crust could be 25 miles thick. But the project was defunded by Congress after only a test bore. The Russians began drilling on land, above the Arctic Circle, and kept at it for 20 years. In the end, they got 8 miles into the crust without ever reaching mantle. But last year, an international expedition on the Resolution, the drilling ship we discussed on a prior episode, set out for the Atlantis Massif. Discovered in the seventies, it’s a huge bulge that rises 14,000 feet above the mid-ocean seafloor. Here, the ocean crust is even thinner, separating into layers as it spreads apart, exposing deep rock that is normally far below Earth’s surface. By drilling less than a mile into this spreading area, the Resolution finally tapped into mantle and brought core samples to the surface—a geologic first, 66 years in the making!

How Planets Get Moons

The Moon has inspired humans for countless generations. Among moons, ours is large, about a quarter the size of Earth. But we have only one. Other planets have many. And some have none. Where do they come from, and how do planets acquire them? Our moon is unique in the solar system. It came from an impact, when an asteroid the size of Mars slammed into Earth 4 billion years ago and smashed off a body that would become the Moon. Other moons are ancient astral bodies that were created along with the planets when the solar system took shape. Still more are former asteroids, which passed near enough to a planet to be captured in its orbit. Small planets closer to the Sun have small gravitational fields. In order to trap a passing asteroid, these would have to combat a stronger gravitational pull from the nearby Sun. For this reason, Mercury and Venus have no moons. Large planets farther from the Sun have stronger gravitational fields that can more easily overcome a weaker pull from the distant Sun, so they have many moons—95 for Jupiter and 146 for Saturn—more than any other planet. Some of those moons are nearly the size of Earth, may have oceans, and may even have undersea life, as we’ve talked about in prior episodes. These moons may be targets for future space missions, inspiring humans of future generations.

Orangutan, Heal Thyself

For many thousands of years, humans have used medicinal plants to help heal wounds. It turns out, some of our primate relatives may have, too. In Indonesia, scientists observed a large male orangutan with an open wound on his face. To their surprise, he sought out a special plant called akar kuning that orangutans usually do not eat. He consumed a large quantity of leaves, then chewed more into a paste, applied it to the wound and left it there. Within five days, the wound had closed. Within six weeks it was gone, with hardly a scar. Local folk healers have long recognized that akar kuning has medicinal properties. Modern chemical analysis has found it contains antibacterial, anti-inflammatory, antifungal and antioxidant compounds. Somehow the orangutan knew this too. And he’s not alone. Orangutans in Borneo have been known to rub other types of chewed leaves on their arms, perhaps to relieve sore muscles. Surprisingly, there are many examples of animals self-medicating with plants. Dogs eat grass and chimps eat bitter herbs to soothe their stomachs. Canada geese eat whole leaves to expel tapeworms. Some rats line their nests with aromatic plants, likely to fumigate parasites. Ancient Greeks, Egyptians and Arabs studied animals’ medicinal use of plants to inform their own. What more might we learn today from animals’ plant choices in the wild?

Life in Hydrothermal Vents

In the deepest, darkest ocean, caustic, superhot water teems with life. In the rest of the ocean, the food web is built on photosynthesis. Phytoplankton takes in sunlight and carbon dioxide to give food and oxygen to everything else. But with no sunlight, these deep ocean communities thrive by chemosynthesis—they consume chemical compounds. In the 1970s, scientists were amazed to discover previously unknown species of shrimp, clams and tube worms living on so-called black smokers. These are hydrothermal vents, where water charged with sulfides by volcanic rocks in Earth’s crust comes gushing out at hundreds of degrees. Specialized bacteria take in volcanic CO2 and convert it directly into organic compounds. These live symbiotically within, or are eaten by, the larger creatures there. On the Atlantis Massif, discussed in a prior episode, scientists discovered a new kind of chemosynthetic community. Here, 200-foot-tall white chimneys of calcium carbonate spew near-boiling water that’s almost as alkaline as Drano and rich with hydrogen and methane—which microorganisms within the chimneys have evolved to consume. Scientists now wonder if dark oceans on other planets or other moons within our solar system, may have hydrothermal vents … which could host their own life forms.

Earth’s Billion-Year Mystery

When the first geologists explored the Grand Canyon, they discovered a billion-year mystery that we still haven’t solved. John Wesley Powell, on his 1868 expedition, called the mile-high canyon walls the “The Library of the Gods” – where he saw 2 billion years of Earth’s history piled in rock layers one atop the other … Except, he realized, there were hundreds of millions of years of rock layers missing! Later geologists found this great "unconformity" -- a break in the geologic rock record -- everywhere. All around the world, the same billion years of rock was simply … gone. What happened? One hypothesis holds that, long ago, when Earth was repeatedly covered in ice for many millions of years, glaciers slid and moved over continents and abraded them down by a mile or more. Another hypothesis relates to heat. For about half a billion years, all of Earth’s land surface was concentrated in one supercontinent called Rodinia. With fewer outlets for Earth’s mantle heat, Rodinia would have expanded and uplifted by a few miles. Erosion before, during and especially following that uplift could have stripped away a mile of rock. More likely, it was a combination of events that washed billions of tons of eroded minerals into the ocean – to enrich and support the Cambrian Explosion of Life that happened just after. A billion-year mystery that eventually led to ... us.